1. Field of the Invention
The invention relates generally to electronic sensors, and particularly to such sensors adapted to electrically interrogate small particles suspended in a fluid carrier medium.
2. State of the Art
Pioneering work in particle detection by measuring impedance deviation caused by particles flowing through a small aperture between two containers of conductive fluids is disclosed in U.S. Pat. No. 2,656,508 to W. H, Coulter. The inventor's name is now associated with the principle of particles causing a change in electric impedance as they occlude a portion of the aperture. Since publication of his patent, considerable effort has been devoted to developing and refining sensing devices operating under the Coulter principle. Relevant US patents include U.S. Pat. No. 5,376,878 to Fisher, U.S. Pat. No. 6,703,819 to Gascoyne et al., U.S. Pat. No. 6,437,551 to Krulevitch et al., U.S. Pat. No. 6,426,615 to Mehta, U.S. Pat. No. 6,169,394 to Frazier et al., U.S. Pat. No. 6,454,945 and U.S. Pat. No. 6,488,896 to Weigl et al., U.S. Pat. No. 6,656,431 to Holl et al., and U.S. Pat. No. 6,794,877 to Blomberg et al. patent application 2002/117,517 to Unger et al. is also relevant. Each above-referenced document is hereby incorporated by reference, as though set forth herein in their entireties, for their disclosures of technology and various sensor arrangements.
While considerable progress has been made in sensor technology, room remains for improvement to sensors adapted for interrogating particles in conductive fluid that are low in cost, permit sample manipulation, and/or ensure accurate selection of a sample volume. It would be an improvement to provide a sensitive and accurate sensor embodied on a cartridge that is sufficiently low in cost to permit its disposal after a single use. It would be another improvement to provide such a cartridge permitting selection of a defined sample volume. A further improvement would provide a cartridge including bubble detecting and removing structure. A still further improvement would provide such a cartridge including reagents disposed to interact with the sample fluid to permit manipulation of a sample, such as diluting, washing, or reacting. A still further improvement would provide such a cartridge that is additionally structured to permit separation of selected particles from the population introduced as a “raw” sample.